The aphid Dysaphis ranunculi causes a gall on the leaves of Hawthorns. These yellowish galls cause the leaf to turn down like an upturned boat, and contain deep grey waxy aphids. The galls may be flushed rosy pink.  It alternates its host between Hawthorns and Ranunculus species but is most often recorded on Hawthorn.

Other Dysaphis cause similar galls, and the vacated galls may also be used by aphids of other species.  The fungus Taphrina crataegi can cause similar blisters and bulges on Hawthorn in April/May

Gall Adult

https://influentialpoints.com/Gallery/Dysaphis_ranunculi_hawthorn-buttercup_aphid.htm

Check that waxy grey aphids are present.  It is difficult to distinguish this gall from D crataegi on Hawthorn, and expert advice should be sought

Wherever Hawthorns are present.

May and June.

Status in Britain not known.

Status in Leicestershire and Rutland not known.

https://influentialpoints.com/Gallery/Dysaphis_ranunculi_hawthorn-buttercup_aphid.htm